An LED element is known that includes a crystal layered structure composed of a Ga2O3 substrate, an AlN buffer layer and a GaN layer (see e.g. PTL 1). In PTL 1, the GaN layer is formed by growing a GaN crystal on the AlN buffer layer under the temperature condition of 1050° C.
In addition, in PTL 1, the AlN buffer layer is formed on the Ga2O3 substrate so as to completely cover the upper surface of the Ga2O3 substrate, and the GaN layer is formed on the AlN buffer layer. The crystal quality of the GaN layer can be improved by forming the AlN buffer layer.
Also, the manufacturing process of the semiconductor element disclosed in PTL 1 is conducted such that a surface of the Ga2O3 substrate is subjected to a nitriding treatment before forming the AlN buffer layer to grow the GaN crystal on the Ga2O3 substrate.